Dogs and inanimate objects will be used as mother substitues for rhesus monkeys. The monkeys live continuously in outdoor kennels with their substitute mothers and receive daily exposure to complex environments designed to encourage a broad range of instrumental activities. One group of monkeys is raised with dogs that are free to roam within these environments. A second group of monkeys is also raised with dogs, but the dog is restricted to one area of the complex environments. The third group of monkeys is raised with inanimate surrogates, placed in one location in each of the complex environments. In this design the monkeys whose dogs are restricted are the pivotal group. Comparing this group with monkeys whose dogs are free to roam will establish the effects of different patterns of maternal behavior in the complex environment. Comparing this same group with monkeys raised with cloth surrogates will establish the effects of living vs. inanimate mother substitutes. Assessment procedures will focus initially on the attachment process (strength, specificity, perceptual aspects), then will extend to general aspects of emotional responsiveness, problem-solving behavior, and social competence.